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NAP1L1 has been shown to function in the life cycle of several DNA virus and retrovirus. However, whether NAP1L1 regulates hepatitis C virus (HCV), a positive-stranded RNA virus, remain to be elucidated. In this study, we identified NAP1L1 as a novel binding partner for HCV NS3. Our results suggest that NAP1L1 contributes to HCV entry, but not viral replication. These findings provide mechanistic insight into the role of NAP1L1 in HCV life cycle and extend the role of NAP1L1 to RNA virus.

Chikungunya virus (CHIKV) is a re-emerging mosquito-transmitted RNA virus causing joint and muscle pain. Although the protein-protein interactions (PPIs) between nonstructural proteins of CHIKV have been extensively established, the complete CHIKV intraviral interactome remains to be elucidated. In this study, we examined all possible CHIKV intraviral PPIs by immunoprecipitation and constructed the intraviral interactome of CHIKV. We reported 19 novel PPIs including the homo-oligomerization of TF. Disulfide bonds promoted the oligomerization of CHIKV TF protein. 2-BP, a palmitoylation inhibitor reduced the palmitoylation of TF and increased TF oligomerization. A quadruple mutant of Cys33, Cys35, Cys41, and Cys43 in TF blocked its palmitoylation and reduced oligomerization. Furthermore, we determined the association of TF with nsP1 and nsP3 in a palmitoylation-dependent manner. Construction of intraviral interactome of CHIKV provides the basis for further studying the function of CHIKV proteins., Highlights • An intraviral interactome of CHIKV proteins is constructed. • CHIKV TF is homo-oligomerized. • CHIKV TF is palmitoylated. • TF interacts with nsP1 and nsP3 in a palmitoylation-dependent manner.

Viral protein 2C plays a critical role in EV-A71 replication. The discovery of 2C binding proteins will likely provide potential targets to treat EV-A71 infection. Here, we provide a global proteomic analysis of the human proteins that interact with the EV-A71 2C protein. TRIM4, exportin2, and ARFGAP1 were validated as 2C binding partners. Further functional studies revealed that TRIM4, exportin2, and ARFGAP1 were novel host dependency factors for EV-A71. Moreover, enteroviruses’ 2C family proteins interacted with exportin2 and ARFGAP1. In conclusion, our study provides a cellular interactome of the EV-A71 2C and identifies the proviral roles of TRIM4, exportin2, and ARFGAP1 in EV-A71 infection.

Baby hamster kidney-21 (BHK-21) cells are widely used to propagate and study many animal viruses using infection and transfection techniques. Among various BHK-21 cell clones, the fibroblast-like BHK-21/C-13 line and the epithelial-like BHK-21/WI-2 line are commonly used cell clones for alphavirus research. Here we report that BHK-21/WI-2 cells were significantly less susceptible to primary infection by the alphavirus chikungunya virus (CHIKV) than were BHK-21/C-13 cells. The electroporation efficiency of alphavirus RNA into BHK-21/WI-2 was also lower than that of BHK-21/C-13. The growth of CHIKV was decreased in BHK-21/WI-2 compared to BHK-21/C-13, while primary infection and growth of the alphavirus Sindbis virus (SINV) were equivalent in the two cell lines. Our results suggested that CHIKV entry could be compromised in BHK-21/WI-2. Indeed, we found that the mRNA level of the CHIKV receptor MXRA8 in BHK-21/WI-2 cells was much lower than that in BHK-21/C-13 cells, and exogenous expression of either human MXRA8 or hamster MXRA8 rescued CHIKV infection. Our results affirm the importance of the MXRA8 receptor for CHIKV infection, and document differences in its expression in two clonal cell lines derived from the original BHK-21 cell cultures. Our results also indicate that CHIKV propagation and entry studies in BHK-21 cells will be significantly more efficient in BHK-21/C-13 than in BHK-21/WI-2 cells.

Lipid droplets are the place for HCV assembly and ADRP is an abundant lipid droplets-associated protein. However, little is known about the mechanisms how ADRP is involved in HCV life cycle. Here we demonstrate that activation of ARF1 dissociates ADRP from lipid droplets. A constitute active form of ARF1 (ARF1Q71I) promotes HCV assembly. We found that ADRP plays a positive role in HCV replication and a negative role in HCV assembly. Overexpression of ADRP increases the size of lipid droplets, while silencing ADRP reduces the size of lipid droplets. These findings provide new insight into the role of lipid droplets proteins in life cycle of HCV.

Claudin-1 is a hepatitis C virus (HCV) coreceptor required for viral entry. Although extensive studies have focused on claudin-1 as an anti-HCV target, little is known about how the level of claudin-1 at the cell surface is regulated by host vesicular transport. Here, we identified an interaction between claudin-1 and Sec24C, a cargo-sorting component of the coat protein complex II (COPII) vesicular transport system. By interacting with Sec24C through its C-terminal YV, claudin-1 is transported from the endoplasmic reticulum (ER) and is eventually targeted to the cell surface. Blocking COPII transport inhibits HCV entry by reducing the level of claudin-1 at the cell surface. These findings provide mechanistic insight into the role of COPII vesicular transport in HCV entry. IMPORTANCE Tight junction protein claudin-1 is one of the cellular receptors for hepatitis C virus, which infects 185 million people globally. Its cellular distribution plays important role in HCV entry; however, it is unclear how the localization of claudin-1 to the cell surface is controlled by host transport pathways. In this paper, we not only identified Sec24C as a key host factor for HCV entry but also uncovered a novel mechanism by which the COPII machinery transports claudin-1 to the cell surface. This mechanism might be extended to other claudins that contain a C-terminal YV or V motif.

In summary, we propose a model for the role of retromer in HCV replication. Upon HCV infection, retromer may provide double-membrane autophagosomal membranes for HCV replication. Our studies suggested a novel link between retromer and autophagy in HCV replication, which may provide new therapeutic targets for antiviral therapy.

Hepatitis C virus (HCV) entry into hepatocytes is a multistep process that represents a promising target for antiviral intervention. The viral envelope protein E1E2 plays a critical role in HCV entry. In this study, we sought to identify peptide inhibitors of HCV by screening a library of overlapping peptides covering E1E2. Screening the peptide library identified several novel anti-HCV peptides. Four peptides from glycoprotein E2 were selected for further investigation. The 50% effective dose (ED50) was approximately 5 nM for each peptide. Our data indicated that these peptides inhibited HCV entry at the post-attachment step. Moreover, these peptides blocked cell-to-cell transmission of HCVcc and had broad-spectrum antiviral effects on HCVcc. These peptides exhibited combination inhibitory effects on HCVcc infection when combined with IFN-α2b or anti-CD81 antibody. Interestingly, we observed that E2-42 associated with E1 and E2. Our results indicate that E2-42 inhibits HCV entry via E1 and E2. These findings suggest a new avenue for HCV therapeutic development.

Hepatitis C virus (HCV) has infected over 170 million people worldwide. Phosphatidylinositol 4-phosphate (PI4P) is the organelle-specific phosphoinositide enriched at sites of HCV replication. Whether retromer, a PI4P-related host transport machinery, unloads its cargo at HCV replication sites remains inconclusive. We sought to characterize the role of retromer in HCV replication. Here, we demonstrated the interaction between retromer subunit Vps35 and HCV NS5A protein by immunoprecipitation and GST pulldown. Vps35 colocalized with NS5A and PI4P in both OR6 replicon and JFH1 infected Huh 7.5.1 cells. HCV replication was inhibited upon silencing retromer subunits. CIMPR, a typical retromer cargo, participated in HCV replication. Our data suggest that retromer component Vps35 is recruited by NS5A to viral replication sites where PI4P unloads CIMPR. These findings demonstrate a dependence role of retromer in HCV replication and identify retromer as a potential therapeutic target against HCV.

Phosphatidylinositol 4-phosphate (PI4P) is well known to be upregulated during hepatitis C virus (HCV) replication. The role of PI4 kinases in HCV has been extensively investigated. Whether the PI4P phosphatase Sac1 is altered by HCV remains unclear. Here, we identified ARFGAP1 to be a novel host factor for HCV replication. We further show that Sac1 interacts with ARFGAP1 and inhibits HCV replication. The elevation of PI4P induced by HCV NS5A is abrogated when the coatomer protein I (COPI) pathway is inhibited. We also found an interaction between NS5A and ARFGAP1. Furthermore, we identified a conserved cluster of positively charged amino acids in NS5A critical for interaction between NS5A and ARFGAP1, induction of PI4P, and HCV replication. Our data demonstrate that ARFGAP1 is a host factor for HCV RNA replication. ARFGAP1 is hijacked by HCV NS5A to remove COPI cargo Sac1 from the site of HCV replication to maintain high levels of PI4P. Our findings provide an additional mechanism by which HCV enhances formation of a PI4P-rich environment. IMPORTANCE PI4P is enriched in the replication area of HCV; however, whether PI4P phosphatase Sac1 is subverted by HCV is not established. The detailed mechanism of how COPI contributes to viral replication remains unknown, though COPI components were hijacked by HCV. We demonstrate that ARFGAP1 is hijacked by HCV NS5A to remove COPI cargo Sac1 from the HCV replication area to maintain high-level PI4P generated by NS5A. Furthermore, we identify a conserved cluster of positively charged amino acids in NS5A, which are critical for interaction between NS5A and ARFGAP1, induction of PI4P, and HCV replication. This study will shed mechanistic insight on how other RNA viruses hijack COPI and Sac1.